Conventionally, various terminal assemblies have been proposed for measuring instruments, and, for instance, the applicant of this application has previously proposed a novel structure in Japanese utility model application No. 2-87524.
According to this structure, as shown in FIG. 7, a nut member 3 formed by bending a relatively thick electroconductive plate into the shape of letter-C is secured inside a terminal spring member 1 likewise formed by bending a thin electroconductive plate into the shape of letter-C. The terminal spring member 1 thus incorporated with the nut member 3 is retained by a casing 7 by engaging spring pieces 5a and 5b cut out and lifted from the two arms 1a and 1b of the terminal spring member 1 with engagement portions 7a and 7b of the casing 7. A terminal screw 9 is threaded into a threaded hole 11 of the nut member 3. A contact piece 13 is formed at a free end of one of the arms 1b of the terminal spring member 1.
When a circuit board 17 is pushed into this terminal assembly guided by an insertion groove 15 provided in the casing 7, a connecting electrode (not shown in the drawing) is resiliently engaged by the contact piece 13. Thus, once an external lead (not shown in the drawing) is connected to the terminal spring member 1, it will be also connected to the circuit board 17.
Furthermore, the entire assembling work is extremely simplified because the nut member 3 can be easily secured in the terminal spring member 1 to join them together, and the threading of the terminal screw 9 is also simple.
However, according to such a terminal assembly for measuring instruments, although some improvement has been made in terms of the simplification of the assembling work, there still is a need for a nut member 3 which is thicker than the terminal spring member 1 to reliably retain the terminal screw 9, and more improvements are desired in the way of reducing the number of component parts and even further simplifying the assembling work.
It is conceivable to integrally form the terminal spring member 1 and the nut member 3 with a thick electroconductive member. However, although it will ensure the terminal screw 9 to be retained in a reliable fashion, the terminal spring member 1 will lose a favorably resiliency that would ensure a reliable and ready electric contact between the connecting electrode of the circuit board 17 received in the casing 7 and the terminal spring member 1 or the nut member 3.
As an additional problem, to avoid interference between the terminal screw and the printed circuit board, it is necessary either to limit the length of the terminal screw or to increase the size of the terminal assembly itself. A short terminal screw is highly inconvenient because the terminal screw may not be unthreaded enough to accommodate an external lead to be connected thereto without entirely unthreading the terminal screw out of the threaded hole. Also, the size of the terminal assembly is desired to be minimized because a large number of such terminal assemblies are normally required to be provided in a limited space.